But how did they make that prediction? In FairVote's attempt to calculate the number of years to gender parity, we have encountered many questions that complicate any prediction. Here are just two.

1. How fast or slow are we moving toward gender parity, and is the rate of change always the same? No, the percentage of women in elected office has not increased at a constant rate. For example, look at the percentage of women in state legislatures since 1971.

Between the 1970s and the mid-1990s, the percentage of women in state legislatures increased at a speedy and relatively constant rate. But from then on, the rate of change decreased to almost nil, with the percentage of women state legislators hovering just below 25% for the last decade. Given the rate of change has decreased so markedly, gender parity may be much, much further away than just a century.

2. How soon will we have gender parity in the Democratic Party? And in the Republican Party? As many organizations, including Political Parity, have noted, the Democratic Party has moved faster toward gender parity than the Republican Party. For example, look at the percentage of Democratic and Republican women in state legislatures since 1981.

Democratic women have increased as a percentage of state legislators from about 7% to 15% between 1981 and 2015. In the same time frame, Republican women have increased as a percentage from about 5% to about 10%. Gender parity in elected office is unlikely to be achieved without both major political parties.

Even beyond these simple graphs, there are many other questions to consider in measuring the years to gender parity. The bottom line is that we should be careful not to underestimate how long it will take. In reality, gender parity is not likely to happen in our lifetimes without structural reforms, such as those presented by Representation 2020.

Representation 2020's State of Women's Representation 2015 (forthcoming) will discuss this topic in detail. Visit www.representation2020.com for more information.